fix: convert schema types to Google uppercase format (fixes #82)

The /compact command was failing with 'Proto field is not repeating,
cannot start list' error for Claude models because tool schemas were
sent with lowercase JSON Schema types (array, object, string) but
Google's Cloud Code API expects uppercase protobuf types (ARRAY,
OBJECT, STRING).

Changes:
- Add toGoogleType() function to convert JSON Schema types to Google format
- Add Phase 5 to cleanSchemaForGemini() for type conversion
- Apply cleanSchemaForGemini() for ALL models (not just Gemini) since
  all requests go through Cloud Code API which validates schema format
- Add comprehensive test suite with 10 tests covering nested arrays,
  complex schemas, and real-world Claude Code tool scenarios

Fixes #82

src/format/schema-sanitizer.js

@@ -564,6 +564,27 @@ export function sanitizeSchema(schema) {
     return sanitized;
 }
 
+/**
+ * Convert JSON Schema type names to Google's Protobuf-style uppercase type names.
+ * Google's Generative AI API expects uppercase types: STRING, OBJECT, ARRAY, etc.
+ *
+ * @param {string} type - JSON Schema type name (lowercase)
+ * @returns {string} Google-format type name (uppercase)
+ */
+function toGoogleType(type) {
+    if (!type || typeof type !== 'string') return type;
+    const typeMap = {
+        'string': 'STRING',
+        'number': 'NUMBER',
+        'integer': 'INTEGER',
+        'boolean': 'BOOLEAN',
+        'array': 'ARRAY',
+        'object': 'OBJECT',
+        'null': 'STRING'  // Fallback for null type
+    };
+    return typeMap[type.toLowerCase()] || type.toUpperCase();
+}
+
 /**
  * Cleans JSON schema for Gemini API compatibility.
  * Uses a multi-phase pipeline matching opencode-antigravity-auth approach.
@@ -642,5 +663,11 @@ export function cleanSchemaForGemini(schema) {
         }
     }
 
+    // Phase 5: Convert type to Google's uppercase format (STRING, OBJECT, ARRAY, etc.)
+    // Only convert at current level - nested types already converted by recursive cleanSchemaForGemini calls
+    if (result.type && typeof result.type === 'string') {
+        result.type = toGoogleType(result.type);
+    }
+
     return result;
 }